AB0552 ELEVATED KYNURENINE LEVELS IN PATIENTS WITH PRIMARY SJÖGREN’S SYNDROME
Authors: H. Apaydin, C. Bİçer, E. F. Yurt, M. A. Serdar, I. Dogan, S. Erten
Journal: Annals of the Rheumatic Diseases (2022)

Background Sjögren’s syndrome (SS) is a chronic autoimmune systemic inflammatory disease of unknown origin that predominantly affects the exocrine glands (mainly salivary and lacrimal glands). Primary Sjögren’s syndrome (pSS) is a disease whose etiology is not yet fully understood, as in most autoimmune diseases, where genetic, epigenetic and environmental factors are hypothesized to play to the pathogenesis of the disease. Metabolism of tryptophan (Trp) via the kynurenine (Kyn) pathway has been proposed to act a substantial role in inflammatory processes. Objectives In the present study, we investigated levels of Trp and its metabolites in the Kyn pathway in patients with pSS and in healthy controls. Also, the relationship between Trp metabolites and laboratory parameters, disease activity was evaluated in patients with pSS. Methods The study included 34 pSS patients and 42 healthy individuals, and serum Trp and Kyn concentrations were measured by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Trp degradation was predicted using the ratio of Kyn and Trp concentrations (Kyn/Trp). The EULAR Sjögren’s syndrome disease activity index (ESSDAI) and the EULAR Sjögren’s Syndrome Patient Reported Index (ESSPRI) were used to evaluate pSS activity. Results In our study, the mean serum Trp concentration was found to be considerably lower in the pSS group compared to the control group (p= 0.001). The levels of Kyn (p= 0.019) and Kyn/Trp ratio (p &lt;0.001) were significantly higher in the pSS group compared to the control group (Table 1). Trp concentration was negatively correlated with physician global assessment (r=-0.568, p&lt;0.001), positively correlated with albumin (r=0.384, p=0.025) and hemoglobin (p=0.396, r=0.020). The Kyn/Trp ratio was negatively correlated with CRP (r=-0.369, p=0.032). There was no correlation between the Trp pathway and disease activity parameters ESSDAI and ESRPI. Table 1. Comparison of the kynurenine pathway results of patients with Sjögren’s syndrome and the controls Sjögren’s syndrome (n=34) median (IQR) Control(n=42) median (IQR) p Kynurenine (ng/ml) 485 (378-601) 386 (356-496) 0.019 Tryptophan (ng/ml) 10660 (9160- 12282) 12258 (11442-14711) 0.001 Kynurenine/tryptophan ratio (%) 4 (3-6) 3 (3-4) &lt;0.001 *Mann-Whitney U test Conclusion In conclusion, we found that kynurenine pathway metabolism was altered in patients with pSS. This suggests that tryptophan metabolism may be closely linked to the disease pathogenesis of pSS. References [1]Stefanski A-L, Tomiak C, Pleyer U, Dietrich T, Burmester GR, Dörner T. The diagnosis and treatment of Sjögren’s syndrome. Deutsches Ärzteblatt International. 2017;114(20):354. [2]Maldini C, Seror R, Fain O, Dhote R, Amoura Z, De Bandt M, et al. Epidemiology of primary Sjögren’s syndrome in a French multiracial/multiethnic area. Arthritis care &amp; research. 2014;66(3):454-63. [3]Moffett JR, Namboodiri MA. Tryptophan and the immune response. Immunology and cell biology. 2003;81(4):247-65. [4]Schroecksnadel K, Winkler C, Duftner C, Wirleitner B, Schirmer M, Fuchs D. Tryptophan degradation increases with stage in patients with rheumatoid arthritis. Clinical rheumatology. 2006;25(3):334-7. Disclosure of Interests None declared